defense official tells cnn, quote, we think they are preparing for a test. we are watching it all as closely as we can. it would be the third north korean nuclear test. commercial imagery shows a tunnel where the test could happen and a bunker to shield equipment and personnel during a test. u.s. government satellites are picking up vehicles and personnel at the nuclear test site, indicating preparations are underway. and a further indication to the u.s. that north korea's ruler is not changing course. >> i think with a new, young leader, we all expected something different. we expected him to focus on improving the lives of the north korean people. >> north korea's state media this week accused the use of nuclear blackmail and said it had no choice but to be defended by their own efforts. on a practical basis, the u.s. can do nothing to stop the underground test. the only realistic option is more condemnation from the united nations once it happens. but it tooks weeks to get a resolution after last month's launch of a rocket by pyongyang. >> the u.n. securi